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Backfire fix

M

micha

Just got it firing!
Joined
Nov 9, 2010
Messages
14
For those of you interested in fixing that annoying lean backfire for your 1200 Sport (or Vintage or Norge or any Lambda probe equipped machine) here a little trick you can do to help your bike.

The science behind this is quite simple and this is commonly done on lightly modified cars. Colder air is denser and for that reason the mapping is slightly richer at colder temperatures. Airplane mechanics know this principle very well. So, we need to tell the ECU the air temperature is slightly lower.

Relevant for Guzzisties, all injected Moto Guzzies use the same air temp sensor part #30729330. Upping the resistance 2k Ohms lowers the perceived temperature signal about 20 degrees Celsius. This in turn richens up the mixture slightly. It works well on all stock bikes but this should be limited to 02 sensor bikes since earlier production year Guzzies have open loop injection systems allowing for manual mixture adjustments.

I have done this on a few 1200 Sports and it works well. Stelvios too but the difference maybe wasn't as dramatic on 8 valve machines. On most vehicles 02 sensor circuits are generally active at idle, at decel and at steady up to 1/4 throttle openings and this is where the difference is most noticeable.

Before you proceed with this little fix be aware that your bike should be tuned, throttle bodies synched and there should be no air leaks anywhere. There is no need to disconnect the idle control valve as it is quite useful on cold mornings.

Also, you are doing this for use on race tracks and not on public roads as this modification alters exhaust emissions slightly.

Lastly any modification you do to your bike is your personal responsibility that you accept at the time of deciding to modify it.

DIY:

At your local Radio Shack you can pick up a 1/4 Watt 2200 Ohm resistor for 99 cents. They come in a pack of 5, you'll need one and you can save the rest for friends overseas or across the street who end up wanting to try this.

On a Sport 1200 under the fuel tank, on top of the air box there is a connector leading to the air temperature sensor. Connector has two wires one of them is black/pink. Solder the resistor in line of that wire, make sure to insulate it with some permanent type shrink tubing. Button it up and take your bike for a ride!

Trough models this wire might change colors so do your homework before you start the work.

Greeting from Seattle and cheers!
:)

PS: Next time I'll have better pictures, promised.
 

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If this causes the mixture to run richer, would this then make the bike run cooler? Also, has anyone done this with a Norge 2V engine yet? A .99 resistor would be cheaper than an ECU reflash job.....
 
This will work on openings/closings of the throttle and open loop map territory.
On usual steady throttle openings the ECU looks at the lambda sensor to make the AFR 14.7 whatever the temp sensor reports or not, I suppose. So no cooler cruising.
This is what memjet alike modules basically do.
Also, it may mess up a little the open loop behavior, depending on air and gasoline temperature, but not by much.
 
Thanks micha!

I read something like this in an Italian forum. They just chose to relocate the air sensor out of the air box.
I may give this a try.

Nick
 
Micha, thanks very much for sharing this information it is much appreciated.

I have only one query / concern with this mod. When the engine is richened up, will it be too rich on really cold days?

BMW V8s in the 1990s had a nickasel bore (same as late model guzzis I understand), the engines ran very rich when cold which caused a phenomenon called "fuel wash" (http://www.hastingsmfg.com/ServiceTips/fuel_wash.htm) which damaged the bores and required a rebuild.

Now I am sure this richening process is not going to make the engine run rich enough to do this damage, but I am concerned the at cold temps it may run too rich with the bike not running properly with this mod, what do you think?

Thanks once again for sharing this knowledge,

Jason
 
The likelyhood of it running cold enough for long enough for bore wash to be an issue is very remote. While I'm not certain of this because we are given next to no information about it I think the warm up cycle has two major controling influences. The sensors for both engine and air temperature and also a timed 'Decay curve' that will drop out the enrichening function quite rapidly.

Early 8V Grisos tended not to like to idle up to get warm, running too rich and eventually stalling if not ridden off. after the first map upgrade this problem disappeared and I think this was probably down to changes being built into the warm-up cycle decay curve.

Pete
 
Regrettably I don't have any reliable info on fuel mileage (is there such a thing as reliable fuel mileage info?). One thing is for sure, there is no free lunch in physics so something will have to pay with this fix - like fuel consumption. Question is how much - probably very little. Do our bikes consume more fuel in Alaska, Norway or Sweden where the air temperature is 20 degrees C colder on average? Probably so but the amount is probably not very significant.

I am not familiar with Memjet but it sounds like an adjsutable resistor. What kind of fuel mileage people report with it, do we know?

Like Pete, I have no real information on cold start parameters on these bikes. They don't have to pass emissions cold so the engineers usually make a sloppy cold start. They just make sure the thing runs. On pre O2 sensor bikes cold start was something like 20% more fuel for first 500 crank revolutions or so. Cold start richness on colder days hasn't been a problem with this fix this far. I tried it multiple times at freezing, seemed fine. I don't have the tools to quantify the increase in fuel percent wise but we could calculate air density per degrees of temperature and translate that into percentage fuel increase or decrease. This assuming that Guzzi engineers follow air density tables when they write maps. Just kidding :p , I think Guzzi factory actually farms out their fuel injection work.

Air density from coldest to warmest temperature at sea level generally varies by about 7%. That should give us some idea of how much of a percentage fuel change this resistor fix provides. 2-3% maybe?

Jason, as far as my knowledge goes wash down has a rare occurrence, last one I saw was on a 20 year old iron bore bike. That thing was beat! In my opinion wash down has more to do with crude carburation, cold engine temperatures and old and worn cylinders. I don't think that will be the case here since fuel increase in this instance is marginal and our bikes have Nickasil cylinders (since LM3 I think).
 
Just a thought.
I don't have the ECU sequences to confirm but wouldn't it have the same results as if you were to adjust the "Fuel Trim" on the VDST software.
(For people that have the 5AM ECU software of course)

All I can confirm is that when I boost the fuel trim value .... it does eliminate the pop and the bike runs richer.
 
The resisitance of the sensor at 20C is 3750 ohms so by increasing the resistance by 2200 ohms to 5950 it will fool the ecu into thinking the air temperature is 10C. (taken from MM Competitions Systems tech sheet for the sensor)_
On this basis if I ride the bike without the mod at 10C surely I should notice reduced backfiring/popping?
 
davem said:
The resisitance of the sensor at 20C is 3750 ohms so by increasing the resistance by 2200 ohms to 5950 it will fool the ecu into thinking the air temperature is 10C. (taken from MM Competitions Systems tech sheet for the sensor)_
On this basis if I ride the bike without the mod at 10C surely I should notice reduced backfiring/popping?
Click to expand...

surely there will be a difference between how the engine runs at 20C when fooling the fuelled into believing it is 10C and how it runs when it is 10C and its fuelled for 10C (ignoring for this purpose other things like altitude) .. but I sure aint no expert in this field :whistle:

Art B1100 + PCV
 
Correct me if I'm wrong.

Given the temperature is 20ºc
I agree that if you are fooling the ECU in thinking its 10ºc the ECU will inject more fuel.
In the close loop condition the lambda sensor will try to adjust to its predetermined program data.
Therefore the lambda ........(at 20ºc) seeing a rich AFR value will decrease the fuel injection where in reality causing a leaner mixture …… rough idle.
 
Thanks for the thread Micha. I performed this mod on my B1200 this morning and apart from the fiddly fuel line connection all went well. Can't road test it yet as it's pouring rain and stinking hot where I am but I'll post again when I get a chance to ride.

Just wondering, could this mod affect the ability to tune the motor with the laptop thingies ??

Cheers :lol:
 
Rode it for an hour today. No improvement at all in the popping/farting.

Oh well, at least it didn't cost much and I learned how to do the tank thing

Cheers,
 
I too tried this on my bike. When the air temp was in the low 20s - all seemed OK. When temp got into the 30s - ran like a sick pig! I used a 2.7K resistor. Popping decrease was noticeable when cold but not really a marked improvement.

I will continue to experiment with different values - I now have a switch that will allow no resistor, 2.7K Ohms and another value yet to be selected - probably around 13.5K Ohm (2 2.7K in parallel). this will give original air temps, 10 degree less and around 4 degree less all at the flick of a switch on the dash.

I would not recommend doing this at all as the net gain is dubious at best and probably just uses more fuel for not performance gain.

Stay tuned...
 
Hi Guys,
On my 07 Breva 1100 I had awful backfiring on overrun and the bike would often stall when coming to a stop at say a set of lights. Everything was spot on, TPS, tappets, plugs, engine/air temp sensor and injector balance using a homemade manometer, even with a stepper motor bypass fitted. I had a feeling it was fuel related as it only happened after the engine had warmed up.
Anyway after much searching I came across this link, (see below) followed the instructions and set mine to 6.6 degrees and it has solved all my problems, I have even put the stepper motor back in. Fuel consumption is still good at around 5.3 Lit/100Km on a run.
Cheers Kevin

Title: Re: Griso/Breva ECU questions
Post by: John in PA on March 02, 2009, 05:52:51 AM

My understanding is that improved maps for late model bikes are now, or soon, available to be downloaded from tha Axone. I don't know if they totally eliminate the problem, but I believe they're supposed to substantially address the problem.

A while back I devised a way to fool the ECU into resetting the TPS voltage and enrichening the bottom end slightly which decreases popping on decell till a more permanent fix is found. Here's a cut-n-paste from my recent post on this procedure. You need Technoresearch VDSTS or Axone to do this.


The tuning software sets the TPS voltage to 4.6 degrees at idle. If you have access to technoresearch or axone, you can force the computer to reset the TPS a couple degrees high to richen the mixture slightly. The TPS is on the right throttlebody, the adjustment for balancing the throttle bodies is on the left side of the bar that links the two TB's.
1. verify that throttle bodies are balanced, if not, adjust before continuing.
2. Hook up software, read, and adjust if necessary, throttle bodies to 4.6 degrees.
3. With software still hooked up, observing tps voltage, UNBALANCE the TB's , dropping the reading by a couple degrees, say down to 3 degrees plus/minus. Do not adjust the allen screw on the left that acts as a throttle stop for both sides, only the adjuster on the linkage bar connecting the tb's.
4. Once the new TPS reading shows, reset the TPS baseline back to 4.6 degrees.
5. now rebalance the TB's and recheck TPS setting displayed. Should be 6-6.5 degrees. If not, repeat steps 3,4,5 of above procedure with minor tweaking of the unbalance setting till desired voltage appears after rebalance.

The new higher baseline voltage tricks the computer into thinking the throttle is slightly open, so it will supply more fuel.
Note: If you set the baseline TPS too high (like 7-ish?), then the computer starts to advance the timing and idle will start to race. If that happens, just decrease the reset baseline a bit.

Note: Jason Speaker told me that the latest Axone software update has an alternate mapping for all the recent FI bikes, if you get the computer remapped, it may eliminate the need for this work-around (or maybe not??)

Hope this helps. I figured out the procedure myself, and have gotten good feedback from those that have tried it. It may not totally eliminate popping, especially if you have a free-flow mufler installed, but it reduces it considerably till a better map, or powercommander, etc, becomes available.

http://wildguzzi.com/forum/index.php?ac ... ic=23916.0
 
Having read the various thoughts on the problem and observed on my Breva 1200 where the backfing occurs i.e. as the revs drop past the 4000rpm mark. it seems the worst of the backfiring occurs on the transtition from open loop back to closed loop. in other words where the mixture gets leaned off for the emissions tests.
On this basis I am fitting a Fat Duc and sticking the bike on the local dyno (weather and holidays permitting).
No doubt there will be a comprimise between reducing the backfiring and getting the AFR somewhere near, but so be it.
I am running a GPR exhaust and a Sprint compeitition filter so it will be interesting to see what the open loop fuelling will be doing, which of course the Fat Duc can't change.
My goal is really only to reduce the backfiring as the bike runs fine with the above setup so any other improvements will be a bonus.
Anyone got any thoughts where the closed loop AFR fuelling should be?
 
Start in the middle and go from there. I found the FatDuc quite good in ensuring the low speed/low throttle roll on actually rolls on instead of jerking on - same with roll off. Doesn't affect the backfiring one iota
 
Kevin, yes the backfire can be tuned out with resetting of the TPS. Lower throttle idle opening for less air at decel and reset TPS or as you described but the idea here is to provide something that anyone can do at home with little to no money upfront and some fun in the garage.
Highest air temperature I tried this at is 22C at sea level on a fully serviced stock bike with minor annoying backfre and it worked great. Tried it on a unit with a Mistral muffler and it worked some but it wasn't the silver bullet. I'll have to wait till summer to try it out in hot weather. We get like 5 days per year of 30C + here. :cry:
For very persistent backfire a diode can be used to lower Lambda sensor feedback 0.5VDC but I haven't experimented with that much yet on Guzzies, I want to have a wide band 02 sensor on hand when I am doing it for comparison.
 
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